The increases in sensitivity of ultra-high field (3 and 4T) body MR imaging have been limited by the lack of efficient body RF coils to provide a uniform transmit and receive fields needed for uniform volume coil or receive-only surface coil imaging. In this proposal will demonstrate the feasibility of a high efficiency elliptic volume coil transmitter for use with receive-only surface coils for torso imaging at 3T and 4T. This system will provide unique capabilities for the body MR imaging. The proposed volume transmit coil will be based on a detunable transmission line resonator of elliptic cross section. The relatively small geometry of this coil will allow the coil to be used as a removable body coil insert efficient enough for use with readily available high frequency RF amplifiers (4-8kW). Preliminary results using a prototype system demonstrate the potential of the proposed approach. In Phase I, we will refine the elliptic body transmitter design, validate the use of PIN diode detuning circuitry to eliminate interactions between the transmit coil and a receive-only coil, validate the lack of significant common mode currents on the receive coil cables, and demonstrate the potential advantages of the system in terms of uniform transmit excitation and increased image sensitivity with human imaging in the heart, liver, and spine. PROPOSED COMMERCIAL APPLICATIONS: We plan to make a detunable elliptic volume coil insert to provide torso imaging for the first time to the over 50 and growing number of 3T and 4T human MR systems. These systems are primarily brain research instruments but the capabilities can be expanded to imaging body organ systems with high sensitivity by the proposed device.